Enhancing image contrast of carbon nanotubes on cellular background using helium ion microscope by varying helium ion fluence

Summary Carbon nanotubes (CNTs) have become an important nano entity for biomedical applications. Conventional methods of their imaging, often cannot be applied in biological samples due to an inadequate spatial resolution or poor contrast between the CNTs and the biological sample. Here we report a unique and effective detection method, which uses differences in conductivities of carbon nanotubes and HeLa cells. The technique involves the use of a helium ion microscope to image the sample with the surface charging artefacts created by the He+ and neutralised by electron flood gun. This enables us to obtain a few nanometre resolution images of CNTs in HeLa Cells with high contrast, which was achieved by tailoring the He+ fluence. Charging artefacts can be efficiently removed for conductive CNTs by a low amount of electrons, the fluence of which is not adequate to discharge the cell surface, resulting in high image contrast. Thus, this technique enables rapid detection of any conducting nano structures on insulating cellular background even in large fields of view and fine spatial resolution. The technique demonstrated has wider applications for researchers seeking enhanced contrast and high‐resolution imaging of any conducting entity in a biological matrix – a commonly encountered issue of importance in drug delivery, tissue engineering and toxicological studies. Lay description Many small particles became a focus of many scientific communities due to their new possible applications in various sciences and industries. Particularly, the particles made up of carbon atoms rolled up into tubes, called carbon nanotubes, which have become particularly important for biomedical applications. For biological and medical research purposes these particles are mixed with various cells in in‐vitro experiments to determine their effect. Due to the particle size and material these particles are made of, it is challenging to image them especially in presence of cells. Use of standard, optical methods of microscopy provide low‐quality images which don't allow to distinguish between particles and the cells. Hence, it became essential to develop new method which could be able to image these small particles and the cells to provide valuable information about the effect of the carbon nanotubes on cells. In this work we present unique method which allows effective imaging and detection of the carbon nanotubes in cellular environment. In this method we use the particular differen